Can only have 1 game at a time with USB loader.

Adding one game to the empty drive works and loads fine, and takes around 15 minutes. When I try to add another game, it seems to work fine, and takes only 2 or 3 minutes. When trying to launch the second game, I get an exception and code dump, the game refuses to load. The same goes for any more games added. I tried with another game starting with an empty drive, it took 15 minutes and worked perfectly. What could be going wrong here?